As a former EMT-Paramedic and person whose hobbies include post apocalyptic role-playing, I keep copies of Where There is No Doctor, Where There is No Dentist, and The Survival Medicine Handbook around (in hardcopy of course).

These are useful.

Take for example, Diarrhea and Dehydration (which throughout history has probably put more people in the ground than all the lead ever fired in anger), Survival Medicine covers making your own rehydration salts, BRAT diet, OTC and RX medicines like Imodium, Zofran, along with natural substances and treatments, like Blackberry Leaf, Raspberry Leaf, and Peppermint (combine any and all that you have into a tea and drink a cup every 2-3 hours). Likewise, there's 1/2 clove of garlic, 1 teaspoon of raw honey, throughout the day is suggested to help; also ginger tea for abdominal cramping.

There are other folk remedies throughout the books and I'm hoping to never have to use any of them!